Since Google is where web users go for information, it makes sense for PR practitioners to pay attention to Google and its best-practice guidelines. To help webmasters, people who run websites and add content online, Google has a set of dos and don'ts. Part of these guidelines relate to PR activities.

Link Schemes
 

Google knows people manipulate links to get ranked, so it has written a thorough checklist of what not to do. The most relevant for PR people is:

Links that are inserted into articles with little coherence, for example:

most people sleep at night. you can buy cheap blankets at shops. a blanket keeps you warm at night. you can also buy a wholesale heater. It produces more warmth and you can just turn it off in summer when you are going on france vacation.

It’s very easy to drop irrelevant links into a press release, hoping it these links will lead to ranking your site. It doesn't help you. At best you may get a short-term ranking boost which will fade away in a number of days and at worst you will get a penalty for having an unnatural link profile. The best way to place links is to make them relevant to whatever is being written about and, if possible, vary the anchor text of the link as much as possible ie, the words used on the link.

Google also talks about not getting links from low-quality directory or bookmark site links
 

It doesn’t explicitly state “Press release sites“, however, a low-quality bookmarking site or directory site is similar to a free press release site because there is no content acceptance process.

As you may know, there are several hundred press release sites you can distribute to (Top 250 Press Release sites) and there are even automated tools for distributing these releases.

Google says: “[do not use] automated programs or services to create links to your site.”

For clients, the idea that you have quickly and cheaply distributed a release across 250 sites seems appealing, however Google does not want you “spamming” the internet with your remarkable content. The best practice here is to avoid any kind of automated mass submission and focus on the top press release sites that Google likes.

Despite the extra work involved, it's probably worth also writing three or four different variations of the release. Google loves variety and has very effective de-duplication filters. So if it sees the same release in several different places, it will devalue the content and links because it sees it as copied or scraped content and so less valuable to their users. More unique releases are better.

One of the latest additions to webmaster guidelines is around hacked content and comment spam. It says:

Engage in good practices like the following:

Monitoring your site for hacking and removing hacked content as soon as it appears.

Preventing and removing user-generated spam on your site.

Google takes site hacking very seriously and it has some very effective tools to work out whether your site is clean or not. If you have been hacked, Google will alert users via webmaster tools, that something is wrong with the site. Therefore a critical task is to set up a Google webmasters account.

If something goes wrong with your site, Google will alert you. You must act quickly to get rid of the infestation. If you leave it more than two weeks, you will be de-ranked because Google does not want this kind of site in its index.

With comment spam, it’s important to monitor your site and to keep it to a minimum. This form of spam is a rich source of poor quality links and enough of these irrelevant links can get you a de-ranking. The rule of thumb is that if the links within your comments are largely going to sites that are thematically consistent with your site, then all is going to be okay.

Most of these pointers are common sense and good site housekeeping. If your site does fall foul of Google, do bear in mind it can be slow to accept your re-inclusion request, so it does make sense to watch the webmaster guidelines and act upon them as they evolve.